The present invention relates to apparatus for severing one or more running webs, strips, tapes or bands of paper, textile material, cardboard, metallic foil, plastic foil or the like, and more particularly to improvements in driving units for so-called cross cutters which are utilized to repeatedly sever a running web, band, strip or tape at desired intervals so that the running material yields a file of discrete plates, panes, panels or sheets. As a rule, such cross cutters employ one or more orbiting knives which are adjacent to the path of lengthwise movement of the material to be severed and each of which severs the web, band, strip or tape once during each of its orbital movements.
It is already known to drive the knife or knives of a cross cutter by a unit which employs universal joints serving to ensure that the knife or knives advance at the speed of the material to be severed in the course of the actual severing operation but that the knife or knives move or can move at a different speed during travel away from and back to the severing station. The angle between the axes of the input and output shafts of the universal joints can be varied by a mechanism which normally includes an angle drive and serves to change the inclination of the input shaft with reference to the output shaft. Reference may be had to East German Pat. No. 51,105 which discloses a driving unit having a drive shaft mounted in parallelism with the shaft for the knife of the cross cutter. The drive shaft is connected with a first bevel gear through the medium of a pair of universal joints and a telescoped shaft between the two joints. The first bevel gear mates with a second bevel gear which is movable lengthwise of a splined shaft. Furthermore, the two bevel gears are connected to each other by a bearing so that the first bevel gear is compelled to share the movements of the second bevel gear in the axial direction of the splined shaft. The latter extends transversely of the knife shaft and of the drive shaft and is connected with the knife shaft by a second pair of bevel gears.
A drawback of the just described patented driving unit is that it is bulky, complex and expensive. Furthermore, the play between the parts which are movable with reference to each other is quite pronounced, especially if one compounds the clearances between all of the elements which are installed between the input element of the driving unit and the knife shaft. Such pronounced play is of no consequence in connection with the production of certain commodities, such as in bag making machines which are specifically referred to in the East German patent. However, an accurate and reproducible cutting operation is quite important in certain other fields, such as in the making of steno pads, exercise books, memo pads and like stationery products wherein the neighboring sheets and/or covers must overlie each other with a high degree of accuracy.